The present invention relates to a clipboard and more particularly to a clipboard having two clamping members spaced substantially parallel to each other for securely clamping articles, such as paper sheets, between one of the two clamping members and a board, wherein the lower clamping member is used to hold an existing bundle of paper sheets on the board while disengaging the upper clamping member to add extra paper sheets to said existing bundle of paper sheets.
There have been known in the art devices, such as clipboards, for clamping together a plurality of loose paper sheets. Since the first patented clipboard, many modifications have been proposed to improve the clamping action of the clamping member on a bundle of paper sheets placed on the board.
The most common kind of clipboard used, such as disclosed in U.S. Pat. No. 2,500,032, granted Mar. 7, 1950 to V. C. Helberg, involves a board, a supporting base fixed to said board via any suitable connecting means such as rivets, a clamping member pivotably mounted on said supporting base with the aid of a torsional spring at a pivotal axle. The clamping member is made of a metal plate which is bent into a downwardly concaving arc. The rear end of the clamping member is provided with an extension at its central portion for use as an actuating lever to pivot the clamping member between opened and closed positions to receive and grip the paper sheets.
A modification of the aforementioned U.S. Pat. No. 2,500,032 is disclosed in U.S. Pat. No. 2,783,062, granted Feb. 26, 1957 to the same applicant. It discloses a clipboard having a clip tiltably mounted on a board by means of a single unitary connecting member formed from spring sheet metal so as to provide a yieldable connection which is entirely devoid of the pivotal axle, torsional spring and other expensive features inherent in the previous structure.
Another kind of clipboard is disclosed in U.S. Pat. No. 4,989,298, granted Feb. 5, 1991 to B.-J. Wang. Disclosed is a paper clip which comprises a pressure bar to drive a clamp plate to clamp on a base plate by means of the operation of a torsional spring. The clamp plate is movably mounted to the base plate by two crank levers. The crank levers have each two conical portions at two opposite ends thereof and respectively made in an extended size so that they can be conveniently fastened in the fixing holes on the base plate and the positioning holes on the clamp plate to firmly secure the clamp plate to the base plate.
When using the known clipboards, such as those disclosed in the above references, a user must use one hand to bias the clamping member to the extent that paper sheets can be readily inserted into the interspace between the clamping member and the board while inserting new paper sheets and holding the previously clamped paper sheets with its other hand in order to prevent them from falling. Such clipboards are not useful for persons such as construction contractors, truckers and cops who work outside most of the time. They have to completely free their hands from any other articles in order to hold the previously clamped paper sheets to prevent them from falling. The same problem occurs in the case where the clipboard is removably fixed to a wall. Obviously, the only way to prevent a user from holding the previously clamped paper sheets is to hold the clipboard horizontally where there is no wind.